Kinetic investigation of the oxidation of bromide ions by cobalt(III). Part 2.—The influence of pyridine and hydrocarbon on the reaction in acetic acid solvent

Abstract

The kinetics of cobalt(III) acetate reduction in acetic acid have been studied under nitrogen at 60–93 °C in the presence of bromide, p-xylene and pyridine. At high p-xylene concentration the initial rate of reaction obeys the rate law [graphic omitted] =k_c[Co^III]²[HBr]²//_{[Co^II][Py]²} with k_c= 0.057 s^–1 at 80 °C and an apparent activation enthalpy of 59.8 ± 5.0 kJ mol^–1. The value of the apparent reaction order with respect to hydrocarbon tends to one at low concentrations. The overall stoichiometry of reduced Co^III and oxidized Br^– ions, ΔCo^III/ΔBr^–, is close to two. The mechanism of reaction involves attack of hydrocarbon by bromine species coordinated to cobalt.